Kernel: Move all tasks-related code to the Tasks subdirectory

Kernel/Tasks/FutexQueue.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/AtomicRefCounted.h>
+#include <Kernel/Locking/Spinlock.h>
+#include <Kernel/Tasks/Thread.h>
+
+namespace Kernel {
+
+class FutexQueue final
+    : public AtomicRefCounted<FutexQueue>
+    , public Thread::BlockerSet {
+public:
+    FutexQueue();
+    virtual ~FutexQueue();
+
+    ErrorOr<u32> wake_n_requeue(u32, Function<ErrorOr<FutexQueue*>()> const&, u32, bool&, bool&);
+    u32 wake_n(u32, Optional<u32> const&, bool&);
+    u32 wake_all(bool&);
+
+    template<class... Args>
+    Thread::BlockResult wait_on(Thread::BlockTimeout const& timeout, Args&&... args)
+    {
+        return Thread::current()->block<Thread::FutexBlocker>(timeout, *this, forward<Args>(args)...);
+    }
+
+    bool queue_imminent_wait();
+    bool try_remove();
+
+    bool is_empty_and_no_imminent_waits()
+    {
+        SpinlockLocker lock(m_lock);
+        return is_empty_and_no_imminent_waits_locked();
+    }
+    bool is_empty_and_no_imminent_waits_locked();
+
+protected:
+    virtual bool should_add_blocker(Thread::Blocker& b, void*) override;
+
+private:
+    size_t m_imminent_waits { 1 }; // We only create this object if we're going to be waiting, so start out with 1
+    bool m_was_removed { false };
+};
+
+}